The pulse wave is usually defined as a wave of blood which is output from the heart and propagates through a blood vessel. For this reason, it is known that various types of medical information can be obtained by the detection of pulse wave and analysis of the detected pulse wave. with the progress of studies on the pulse wave, it has become clear that various types of information, not obtainable only from the blood pressure and the pulse rate, can be obtained by analyzing the pulse wave, collected from the human body, by various techniques, making a diagnosis possible on the basis of these types of information.
The inventors of the present invention remarked the relation between the pulse waveform and its distortion rate in PCT/JP96/01254 (Title of the Invention: DIAGNOSTIC APPARATUS FOR DETECTING CONDITION OF LIVING BODY AND CONTROLLER) and made it possible to diagnose the living condition of a subject by detecting and treating the pulse waveform of the subject, calculating the distortion rate of the waveform and specifying the waveform from the distortion rate.
Here, the relationship between a pulse waveform and a distortion rate which are mentioned in the above application will be described briefly.
First, there are various types of pulse waveforms and the forms are diversified. Here, typical forms of pulse waveforms by the classification of Chinese medicine which is one of a traditional oriental medicine will be described. FIGS. 45A to 45C are the charts showing representative pulse waveforms by this classification.
The pulse waveform shown in FIG. 45A is called a "Ping mai" which is the pulse condition of a normal man in good health. This "Ping mai" is characterized in that, as shown in the figure, the pulse is relaxed, and exhibits a constant rhythm without disruption.
Secondly, the pulse waveform shown in FIG. 45B is called a "Hua mai" which is the pulse condition of a man who shows an abnormality in his blood stream condition. The waveform of a Hua mai exhibits a sharp, rapid rise, and then falls off immediately, the aortic dicrotic notch is deep and at the same time the subsequent peak is considerably higher than that of a Ping mai. It is considered that diseases such as a mammary tumor, liver or kidney ailment, respiratory ailment, stomach or intestinal ailment or inflammation, or some other illness cause the movement of the blood to be very fluent and smooth, which causes this "Hua mai".
Moreover, the pulse waveform shown in FIG. 45C is called a "Xuan mai" which is the pulse condition of a man whose blood vessel wall tension has increased. The Xuan mai is characterized in that its waveform rises steeply and remains at a high pressure state for a fixed period of time without an immediate drop. This "Xuan mai" is seen in diseases such as liver and gall ailments, dermatological ailments, high blood pressure, and pain ailments. It is believed that tension in the automatic nervous system causes the walls of the blood vessels to constrict, decreasing elasticity, so that the effect of the blood pulsation of the pumped blood is not readily expressed, causing this phenomenon.
The ordinate and the abscissa in the graphs of FIGS. 45A to 45C show blood pressure (mmHg) and time (second) respectively.
The relationship between the pulse condition of the pulse waveform and its distortion rated is shown in FIG. 46. Here, the distortion rate d of the pulse waveform is determined by the following equation (1): ##EQU1##
wherein A.sub.1 is the amplitude of a basic wave component in the pulse wave and A.sub.2, A.sub.3, . . . , A.sub.n are the amplitudes of the second, third, . . . and nth harmonic components respectively.
It is therefore possible to specify the pulse condition of the pulse waveform quantitatively from the correlation shown in FIG. 46 if the pulse waveform of a subject is detected and the detected waveform is subjected to FFT (Fourier transformation) treatment to find the amplitudes A.sub.1 to A.sub.n from which the distortion rate d is calculated.
As shown in FIG. 46, when the pulse condition of the subject is judged to be a Hua mai, the distortion rate d is in a range between 0.98 and 1.22. When the pulse condition is judged to be a Ping mai, the distortion rate d is in a range between 0.92 and 1.10. When the pulse condition is judged to be a Xuan mai, the distortion rate d is in a range between 0.73 and 0.94.
In this case, the pulse condition can be judged to be a Hua mai or a Ping mai when the distortion rate d of the pulse waveform is in a range between 0.98 and 1.10. Also, the pulse condition can be judged to be a Ping mai or a Xuan mai when the distortion rate d of the pulse waveform is in a range between 0.92 and 0.94. It is therefore difficult to judge the pulse condition precisely by a conventional pulse wave examination apparatus.
In the meantime, a blood pressure gauge measuring a maximum blood pressure and a minimum blood pressure and displaying these pressures is used in noninvasive detection of blood pressure.
Although the maximum blood pressures or minimum pressures of subjects are alike, there are various types of waveforms for blood pressure. Hence the characteristics of the blood pressure of an individual expressed only by a maximum blood pressure and a minimum blood pressure are insufficient.
The mean blood pressure is an important parameter for knowing the condition of the blood pressure of an individual. The mean blood pressure cannot be obtained only by measurements of a maximum blood pressure and minimum blood pressure.
In sphygmic detection adopted in Chinese medicine or in Indian traditional medicine, a medical examination is carried out by examining the pulse waveform detected by the fingers when a medical examiner presses with an optimum pressing force against a distal position of the forearm from the arteria radialis, that is, a medical examination is conducted by detection of a variation with the pressing force, which variation is felt by the fingers of the medical examiner corresponding to a variation in blood pressure.
In Chinese medicine, for instance, the pulse waveform felt when a proper pressing force is applied to the arteria radialis is roughly divided into three categories, which are designated as a "Ping mai", "Hua mai" and "Xuan mai" respectively as aforementioned. The Ping mai is deliberate and mild and its rhythm is stable and reduced in turbulence. This Ping mai is a pulse image for a man in good health. The Hua mai is the type in which the flow of the pulse is felt to be very fluent and smooth, showing abnormality in the blood stream condition. The Xuan mai is felt to be a straight, tense and long pulse and is regarded to be due to tension or aging of a blood vessel wall.
Such a medical examination method, however, is dependent upon the pulse waveform classified by the sense of the medical examiner posing problems with regard to its objectivity and reproducibility.
The present invention has been conducted in the above situation and has an object of providing a pulse wave examination apparatus which can judge the pulse condition objectively and accurately.
Another object of the present invention is to provide a blood pressure monitor which can indicate blood conditions in more detail than the information of a maximum and minimum blood pressure and can monitor the monitor parameters signifying blood pressure noninvasively.
A further object of the present invention is to provide a pulse waveform monitor which can carry out an examination by the pulse waveform objectively and reproducibly.